Treatment of lignocellulosic material in an alkaline pulping liquor containing anthraquinone sulphonic acid followed by oxygen delignification

ABSTRACT

Lignocellulosic material is treated with an alkaline pulping liquor containing anthraquinone monosulphonic acid, anthraquinone disulphonic acid or alkali metal salts of said acids followed by treatment with alkali metal hydroxide and oxygen.

United States Patent [191 Kenig June 10, 1975 [5 TREATMENT OF LIGNOCELLULOSIC 3,691,008 9/1972 Worster et a1. 162/65 X MATERIAL IN AN ALKALINE PULPING S amue S011 eta LIQUOR CONTAINING ANTHRAQUINONE 3,798,119 3/ 1974 Singh 162/65 SULPHONIC ACID FOLLOWED BY OXYGEN DELIGNIFICATION Inventor: Samuel Kenig, Longueuil, Quebec,

Canada Canadian Industries Limited, Montreal, Quebec, Canada Filed: Apr. 8, 1974 Appl. No.: 459,112

Assignee:

Foreign Application Priority Data References Cited UNITED STATES PATENTS 3/1972 Croon et a1 162/65 FOREIGN PATENTS OR APPLICATIONS 591,702 2/1960 Canada 162/89 OTHER PUBLICATIONS Casey, Pulp & Paper, Vol. I, pgs. 221--230, 236-243 & 259, 1960.

Primary Examiner-S. Leon Bashore Assistant ExaminerArthur L. Corbin Attorney, Agent, or FirmAlexander O. McIntosh ABSTRACT 14 Claims, N0 Drawings 1 TREATMENT OF LIGNOCELLULOSIC MATERIAL IN AN ALKALINE PULPING LIQUOR CONTAINING ANTI-IRAQUINONE SULPI-IONIC ACID FOLLOWED BY OXYGEN DELIGNIFICATION This invention relates to a process for the delignification of lignocellulosic material such as wood, bagasse, straw, etc.

The processing of lignocellulosic material to produce cellulose suitable for the manufacture of paper products involves the removal of lignin and other noncellulosic components such as gums. Reagents that attack lignin without affecting appreciably the cellulose are preferred for this purpose. In the sulphate or kraft process lignocellulosic material is cooked with a mixture of sodium hydroxide and sodium sulphide. In the soda process the cooking is carried out with sodium hydroxide alone. Although these processes are effective in the removal of lignin from lignocellulosic material such as wood, the cellulose component of the material is attacked also to a certain degree, resulting in a lowering of yields and degradation of the product.

In Canadian Pat. No. 895,756 issued on Mar. 21, 1972 to H. E. Worster and M. F. Pudek there is described a two stage soda-oxygen pulping process comprising a first stage sodium hydroxide digestion, followed by defiberization of the product of the sodium hydroxide digestion and a second stage digestion with sodium hydroxide in the presence of excess oxygen. This known process produced pulp in yield comparable to the yield of a conventional kraft process.

It has now been found that lignocellulosic material can be delignified effectively in a two stage process, without intermediate defiberization, comprising a first stage cooking with sulphate or caustic liquor at a temperature higher than used in conventional pulping processes, the cooking being adapted to produce a high yield, followed by a second stage treatment in alkaline medium with oxygen or an oxygen-containing gas under pressure. The cooking periods of the novel process are of the same order as of conventional kraft processes. The novel process provides a pulp in higher yield, of better bleaching response with the production of less pollution than conventional pulping processes.

Thus the main object of this invention is to provide a pulping process that gives an increased yield of cellulosic pulp. A further object is to provide a two stage process that can be carried out as continuous unit operation without an intermediate defiberization step. Ad-' ditional objects will appear hereinafter.

The process of this invention comprises the steps of l. treating lignocellulosic material in a closed reaction vessel with a pulping liquor containing alkali metal hydroxide with or without admixture of alkali metal sulphide at a temperature in the range 160C to 195C for a period of not greater than 90 minutes and preferably not greater than 60 minutes, the temperature and period of treatment being adapted to provide a pulp yield of 55 to 65 percent by weight.

2. displacing the pulping liquor from the lignocellulosic material with water, or an aqueous solution of alkali metal hydroxide, A

3. treating the material in aqueous suspension at a consistency of 2.0 to 30.0 percent by weight for 0.5 to 30 minutes at C to 90C with 2l0' to 20.0 percent by weight of alkali metal hydroxide, and

4. treating the alkaline material in aqueous medium at a consistency of from 3.0 to 35.0 percent by weight with oxygen or an oxygen-containing gas for 10 to minutes at a temperature of 80C to C and a partial pressure of oxygen of 30 to 200 pounds per square inch.

When the lignocellulosic material employed is wood, this is first converted into the form of chips. This step will not be required when the lignocellulosic material is of fibrous form.

The process of this invention can be used to delignify either coniferous or deciduous species of wood. By coniferous is meant species such as pine, spruce and balsam fir. By deciduous is meant species such as birch, aspen, eastern cottonwood, maple, beech and oak. When employed with a high density deciduous wood such as birch it is preferable to employ a longer time to reach maximum cooking temperature in the first stage and to add alkali hydroxide in the second stage while the pulp is at low consistency e.g. 2 to 6 percent. It is desirable to remove 40 to 60 percent of the lignin of dense deciduous woods in the first stage.

When the treatment of the first step is carried out with a pulping liquor containing only alkali metal hydroxide, 14 to 24 percent preferably 18 to 22 percent by weight of this, based on the weight of the lignocellulosic material is employed. Normally the liquor will also contain alkali metal carbonate.

When the treatment of the first step is carried out with a pulping liquor containing both alkali metal hydroxide and alkali metal sulphide 8 to 14 percent, preferably 10 to 12 percent by weight alkali metal hydroxide expressed as effective alkali (TAPPI T 1203 05-61 and 5 to 40 percent, preferably 20 to 30 percent by weight alkali metal sulphide expressed as percent sulphidity (TAPPI T 1203 08-61 based on lignocellulosic material, is employed. This pulping liquor will normally also contain alkali metal sulphate and alkali metal carbonate.

Effective alkali is the sum of all alkali hydroxide in solution expressed as Na O including that formed by hydrolysis of the alkali sulphide, also expressed as Na- O. v

Sulphidity is the total sulphide, expressed as Na O, calculated as a percentage of total titratable alkali, including that formed by hydrolysis of the sulphide, also expressed as Na O.

Since the first step treatment is carried out in a closed reaction vessel at a temperature in the range C to C in the presence of water, the reaction will take place at supra atmospheric pressure.

It has been found that the yield is increased and delignification is accelerated by the addition to the pulping liquor of 0.02 to 2.0 percent, preferably 0.05 to 1.0 percent, by weight based on the lignocellulosic material, of anthraquinone monosulphonic acid or anthraquinone disulphonic acid, or alkali metal salts of said acids, or mixtures of the aforesaid acids and/or salts. The addition of said anthraquinone compounds is most effective when the first step is carried out with a pulping liquor containing alkali metal hydroxide without addition of alkali metal sulphide.

After the first step treatment with pulping liquor the resulting pulp yield will be 52 to 65 percent, preferably 58 to 62 percent by weight, based upon the lignocellulosic material. The kappa number of the material at the completion of the first step will lie in the range 80-130 for "oniferous woods and in the range 40-90 for deciduous woods.

The partially delignified material resulting from the first treatment step is discharged from the pulping vessel and the spent liquor displaced by fresh water or spent liquor from the alkaline oxygen treatment step or white water from a later stage of a papermaking process. By white water is meant process water that has been used for transfer of slush pulp and has been separated from the pulp for re-use in the process. To the material is then added alkali metal hydroxide. The alkali metal hydroxide may be provided in the form of pulping liquor or white liquor" such as used in the first stage of the process. This liquor therefore may contain sulphide, sulphate and carbonate in addition to the alkali metal hydroxide. Preferably there is also added 0.1 to 1.0 percent by weight of the pulp of a magnesium salt such as magnesium chloride or magnesium sulphate. The magnesium salt may be added directly as the salt or as a complex formed with the spent liquor from the alkaline oxygen treatment step.

The alkaline lignocellulosic mateial is then fed without mechanical defiberization into an oxygen treatment vessel. The material is then treated with oxygen or an oxygen-containing gas under pressure.

The product of the oxygen treatment is separated from the spent liquor and washed with water. It will have a residual lignin content of 2 to 6 percent, preferably, 2 to 4 percent of weight of the original lignocellulosic material, corresponding to a yield of 43 to 53 percent by weight.

The alkali metal hydroxide employed as reagent in the process of this invention may be sodium hydroxide or potassium hydroxide. The alkali metal sulphide reagent may be sodium sulphide or potassium sulphide.

The oxygen treated material may be subjected to a bleaching treatment. A conventional bleaching sequence comprising chlorination, alkaline extraction and treatment with chlorine dioxide is sufficient to provide a product having a brightness of approximately 90 units (Elrepho). Alternatively the first bleaching stage may comprise treatment with chlorine dioxide followed sequentially, without intervening washing, by chlorination.

The process of this invention has the advantage that no defiberization is required between the treatment with pulping liquor and the treatment with oxygen. This reduces the amount of equipment required for the process. In distinction to conventional soda pulping which requires cooking periods of several hours the cooking periods of the present invention are of the same order as a conventional kraft process. Employing the process of the present invention wherein the first stage utilizes kraft pulping liquor it is possible to obtain a product in yield which is 6 to 7 percent greater than the yield of a conventional kraft process. When the present process is followed by a conventional bleaching sequence the decrease in yield caused by bleaching is equivalent to the decrease in yield that occurs in bleaching pulp of the same kappa number prepared by the kraft process. In addition, the lessened usage of sulphur-containing reagents results in lessened pollution potential.

The invention is illustrated by the following Examples but its scope is not limited to the embodiments shown therein.

In the Examples the kappa number and viscosity determinations were carried out by the following methods TAPPI Method T-236 M- Kappa Number TAPPI Method T-230-SU-66 Viscosity Tensile (breaking length) TAPPI T-404-M Burst factor TAPPI T-403-M Tear factor TAPPl T-414-M EXAMPLE 1 A mixture of spruce and balsam wood chips was subjected to the following treatment sequence.

1. The chips were cooked with kraft liquor containing 12 percent by weight of effective alkali expressed as sodium oxide and 25% sulphidity and 1.0% of anthraquinone- 2-mono-sulphonic acid based on the weight of wood, the ratio of liquor to wood being 4. The maximum temperature of the cook was 180C and was reached after 60 minutes. The cook was maintained at 180C for 10 minutes. The yield of the cook was 60.9 percent, the product having a kappa number of 104.

2. The partially delignified wood. was washed with water.

3. Without defiberization, the partially delignified wood was impregnated at room temperature with an aqueous solution containing 9.5% sodium hydroxide and magnesium sulphate in an amount containing 0.2% magnesium ion, based on the weight of the partially delignified wood.

4. The alkaline wood was treated in a closed reactor in the presence of water at a consistency of 27 percent, at 1 15C for 50 minutes with oxygen under a partial pressure of 80 psi. The delignified product was obtained with a yield of 51.9 percent based on the starting material, and a kappa number of 30 and a viscosity of 13.1 centipoise.

5. The oxygen-treated product of step 4 was subjected to three bleaching steps: chlorination, caustic extraction and chlorine dioxide treatment.

Chlorination: Pulp at 3 percent consistency by weight treated with 6 percent by weight of chlorine for 1 hour at 24C. Caustic extraction: Pulp at 10 percent consistency by weight treated with 2.9 percent by weight of sodium hydroxide for 2 hours at C. Chlorine dioxide treatment: Pulp at 6 percent consistency by weight treated with 0.6% chlorine dioxide by weight for 3 hours at 70C.

The pulp was washed with water at the completion of each of the bleaching steps.

The product had a brightness of 88.4 (Elrepho) and a viscosity of 11.8 centipoise. The physical properties of the product are shown in the following Table I.

I TABLE 1. The chips were cooked with soda liquor containing 20 percent by weight of sodium hydroxide and 0.1

Freeness Breaking Burst Tear Bulk C.S.F. Length Factor Factor cc/gm percent by weight of anthraqumone-Z- M 5 monosulphonic acid based on the weight of the 500 12,700 103 83 1'33 wood, the ratio of liquor to wood being 4. The maxi- 300 13,300 105 76 mum temperature of the cook was 180C and was reached after 60 minutes. The cook was maintained at 180C for 45 minutes. The yield was 52.5 percent EXAMPLE 2 l0 and the kappa number 84. The Same mixture of Spruce and balsam wood chips 2. Thte partially delignified wood was washed with fresh wa er.

as in Example 1 was subjected to the following treatment sequence. 3. Without defiberization, the partially delignified wood was impregnated at room temperature with an 1. The chips were cooked with soda liquor containing aqueous sohltion Containing 50% sodium hYdr9Xde percent by weight of sodium hydroxide based on and magneslllm S u1phate m an amolmt contammg the weight of wood, the ratio of liquor to wood being 9 magnslum based on the Welght of the 4. Maximum temperature of the cook was 180C and dehgmfied Wood was reached after 60 minutes. The cookwas maim 20 4. The alkalme wood was treatedln a closed reactor in tained at 180C for 60 minutes. The yield was 53.2 the Presence of Wafer at FOHSISteIICY of 27 percelfltl percent and the kappa number 106 at l 15C for 50 mlnutes with oxygen under a partial 2. The partially delignified wood was washed with fresh Pressure of 80 P The delignified Product was water tained with a yield of 48.4 percent based on the start- 3. Without defiberization, the partially delignified ing material, and had a pp number of 28 and a wood was impregnated at room temperature with an cosity of 10.8 centipoiseaqueous solution containing 9.0% sodium hydroxide The xyg nat d P c pulp f s ep 4 aS Suband magnesium sulphate in an amount containing jected to three bleaching steps: chlorination, caustic 0.2% magnesium ion, based on the weight of the parextraction and chlorine dioxide treatment. tially delignified wood. 3O Chlorination: Pulp at 3 percent consistency by 4. The alkaline wood was treated in a closed reactor in weight treated with 5.6% chlorine for 1 hour at 24C. the presence of water at consistency of 27 percent, Caustic extraction: Pulp at 10 percent consistency by at 115C for 50 minutes with oxygen under a partial weight treated with 2.7% sodium hydroxide for 2 pressure of 80 psi. The delignified product was obhou at 65C, tained With a yield o 6- Per based on the Start- Chlorine dioxide treatment: Pulp at 6 percent consising material, and had a pp number and a tency by weight treated with 0.7% chlorine dioxide cosity of centipoiseby weight for 3 hours at 70C.

The oxygen'tl'eated P P p of p 4 was The pulp was washed with water at the completion jected to three bleaching steps: chlorination, caustic f h f the bleaching steps. extraction and chlorine dioxide treatment. 40

Chlorination: Pulp at 3 Percent consistency by The product had a brightness of 87.5 (Elrepho) and weight treated'with 5.6% chlorine for 1 hour at 24C. Caustic extraction: Pulp at 10 percent consistency by weight treated with 2.2% sodium hydroxide for 2 a viscosity of 10.7 centipoise. The physical properties of the product are shown in Table III.

hOLlIS at 65C. TABLE In Chlorine dioxide treatment: Pulp at 6 percent consistency by weight treated with 0.7% chlorine dioxide Freeness Breaking Burst Tear Bulk y Weight for 3 hours at 700C C.S.F. Lelnllgth Factor Factor cc/gm The pulp was washed with water at the completion e leachin ste s. .500 2,700 84 107 1.37 of each ofth b g p 300 13,300 93 98 1.35

The product had a brightness of 88.5 (Elrepho) and a viscosity of 7.3 centipoise. The physical properties of the product are shown in Table II. EXAMPLE 4 TABLE II A mixture of spruce and balsam wood chips was subjected to the following sequence of treatment. Freeness Breaking Burst Te Bulk l. The chips were cooked with kraft liquor containing g Factor Factor cc/gm 12 percent by weight effective alkali expressed as sodium oxide and 25 percent sulphidity based on the 588 i238 3g 3g lg? weight of wood, the ratio of liquor to wood being 4. The maximum temperature of the cook was 180C and was reached after 60 minutes. The cook was maintained at 180C for 15 minutes. The yield of the EXAMPLE 3 cook was 60.4 percent, the product having a kappa The same mixture of spruce and balsam wood chips number of 103.

as in Example 1 was subjected to the following treat- 2. The partially delignified wood was washed with fresh ment sequence. water.

3. Without refining, the partially delignified wood was impregnated at room temperature with an aqueous solution containing 9.0% sodium hydroxide and magnesium sulphate in an amount containing 0.2% mag- The chips were cooked with a kraft liquor containing 15.5 percent effective alkali expressed as sodium oxide and 25 percent sulphidity based on wood, the ratio of liquor to wood being 4. The maximum temperature of As comparison to the results obtained in Examples 1,

2, 3 and 4 which employed the process of the invention 65 nesium ion, based on the weight Of the partially delig- 5 the cook was 170C and was reached after 60 minutes. nified WOOd- The cook was maintained at 170C for 120 minutes. 4. The alkaline wood was treated in a closed reactor in Th i ld f h k w 45,0 percent, the product the presence of water at a consistency of 27 percent, l having a kappa number of 30. at 1 for 60 minutes with Oxygen under a Partial The material was washed with fresh water and subpress e o 80 Pounds p r q r inch- The g 10 jected to a five stage bleaching sequence as follows. fled g s optaliled g i Chlorination: Pulp at 3% consistency by weight treated ase Ont e h fnatena an a a appa with 6 percent by weight of chlorine for 1 hour at number of 25 and a viscosity of 15 centlpolse. i oxygen'treated pioduct pulp of was i Caustic extraction: Pulp as 10 percent consistency by ected to three bleaching steps; chlorination caustic 15 weight treated i h 2 8 rcent by weight of sodium extraction and chlorine dioxide treatment. The conhydroxide for 2 hours at 65C y 1 g i p i g i g g i as 2 3? b Chlorine dioxide treatment: Pulp at 6 percent consisorma p a per n e y tency by weight treated with 1.0% chlorine dioxide weight treated with percent by weight of chlorlne by weight for 3 hours at 0 i 1 h at t t t b Caustic extraction: Pulp at 10 percent consistency by 3 extractlohu p a percen (fonsls Y y weight treated with 0.5 percent by weight of sodium weight treated w1th 2.4 percent by weight of sodium hydroxide for 1 1 hours at o hydroxide for 2 hou at 65 Chlorine dioxide treatment: Pulp at 6 percent consis- Chlorme dioxide treatment: Pulp at 6 percent consrstency by Weight trgated with 03% Chlorine dioxide tency by weight treated with 0.7% chlorine dioxide by weight for 3 hours at I o y Weight for 3 hours 7 The pulp was washed with water at the completion of The pulp was washed with water at the completion each of the bleaching Steps. of each of the hleachlhg p The product was obtained in 41.2 percent yield based The Product was Obtamed 4725 Percent yleld on wood, and had a brightness of 89.0 (Elrepho) and based on wood and had a brightness of 88.5 (Elrepho) a viscosity f 1&8 i i and a Viscosity of cehtipolse- The strength properties of the product are shown in The strength properties of the product are shown in T bl \I Table IV.

TABLE IV TABLE V Freeness Breaking Burst Tear Freeness Breaking Burst Tear Bulk C.S.F. Length Factor Factor C.S.F. Lepigth Factor Factor cc/gm TABLE VI Yield Comparison Between the Process of this Invention (Examples 1 to 4) and a Conventional Kraft Process (Example 5) in Delignification of Coniferous Wood This Invention Control Type of Cook Soda Kraft Soda Kraft Kraft +AMS +AMS Example 2 4 3 l 5 Kappa Number 23 25 28 30 30 Yield on wood 46.7 50.5 48.4 51.9 45 increase in yield compared to control L7 5.5 3.4 6.9 on wood Increase in yield compared to control adjusted to same 4.2 7.2 4.1 6.9 Kappa Number on wood AMS anthraquinone-Z-monosulphonic acid EXAMPLE 5 The same wood (spruce and balsam) was used in all 5 examples.

Adjustment of the yield of the control to a yield corresponding to kappa number of Examplesl to 4 was carried out by interpolation of a plot of kappa number against yield for the wood species in question.

The plot was based upon the relationship Percent lignin 0.15 (Kappa Number) 0.24 disclosed in Some Fundamental Aspects of Oxygen Pulping" by R. Marton, 4th Canadian Wood Symposium, Quebec City, July 4-6, 1973. The initial lignin content of the wood was obtained from Pulpwoods of United States and Canada, I. H. lsenberg, 2nd edition, Institute of Paper Chemistry, Appleton Wisconsin 1951. The slope of the plotted values was 0.332 percent yield per kappa numand25.0 percent sulphidity at a liquor to wood ratio of 4:1. The maximum temperature of the was 180C and was reached in 2 hours. The treatment was terminated when 180C was reached. The yield was 58.1 percent of wood at a kappa number of 42.9.

The product was washed with cold water and split into equal portions A and B. Without defiberization each portion was impregnated with an aqueous solution of 5.6% sodium hydroxide and magnesium sulphate her. The adjusted yield values for the control (Example 10 containing 0.2% magnesium ion based on pulp. Th i 5) are shown in Table V11. pregnation of A was carried out at a pulp consistency LE VII of 3 percent followed by pressing to a consistency of 27 TAB percent. The impregnation of B was carried out at a pulp consistency of 27 percent. 7 Kappa Number Both portions were treated in the same oxygen reac- 23 425 tor at the same time at a temperature of 120C for a peg; 12% riod of 40 minutes at a partial pressure of oxygen of 80 psi.

Portion A had a yield of 93.9 percent with 9.8 per- TABLE II cent of screen rejects based on pulp weight or a yield of 54.6 percent with 4.9 percent of screen rejects based fC fBl h Ch I on wood. The kappa number of the product was 1 1.1, Comparison 0 omposition o eac ing emicas by the Product of this Invention the v1scos1ty 22.2 cps. Portion B had a yield of 90.3 per (Example 1 cent w1th 16 percent screen re ects based on pulp and gzzfiqgg Pmcess weight or a yield of 52.5 percent with 7.7 percent mangle 1 Example 5 screen rejects based on wood. The kappa number was (Control) 12.3, the viscosity 16.6 cps.

Chlorine 6 6 It can be seen that low consistency 1mpregnation is Sodium hydroxide 2.9 3.3 o e effectlve.

Chlorine dioxide 0.6 1.3

EXAMPLE 7 Both products were derived from spruce and balsam wood and prior to bleaching both had kappa numbers 2 l i gg g bnghmess of Nine samples of birch wood chips were delignified in Xamp e to a mess 0 I k f d th order to evaluate the bleaching response and strength Compared c?nventlol 1a ra t pro l 6 properties of the resulting pulps. Four of the samples product of this 1nvent1on required for bleachmgthe were delignified using the process of this invention m f gf i: Sodlum wherein the first stage employed kraft cooking liquor.

hydroxlde an percent e85 c 40 Four additional samples were delignified using the process with first stage cooking with soda liquor. One sample serving as control was delignified by a conventional kraft cookin rocedure. The details of the deli nifi- EXAMPLE 6 g P g cation procedures are shown in Table IX, the bleachlng A sample of birch wood chips was treated with kraft response in Table X and strength properties in Table cooking liquor containing 13.0 percent effective alkali X1.

TABLE 1X First Stage Second Stage Vis- Sample Cooking Alkali AMS I Retention Kappa Yield NaOH Kappa Yield Yield cosity Liquor i Temp. time Number I Number cention wood on wood "C hours of pulp on wood on pulp of pulp on pulp on wood poise 1 Kraft 10.0 180 A 51 61.2 4.5 15 94.0 57.6 23.8 2 Kraft 10.0 0.5 180 1/6 51 64.6 4.5 17 95.0 61.6 20.4 3 Kraft 10.0 170 1% 53 62.1 4.5 17 90.0 56.6 27.6 4 Kraft 10.0 0.5 170 l 53 61.4 4.5 15 90.0 55.7 21.6 5 Soda 18.0 180 1 49 55.0 4.25 ,15 90.5 51.4 12.8 6 Soda 16.0 0.1 180 52 56.6 4.5 16 96.7 54.6 15.2 7 Soda 16.0 170 2 55 57.0 4.5 16 89.7 51.0 15.7 8 Soda 18.0 i 0.1 170 1% 55 58.7 4.5 16 94.4 55.4 14.5 9 Kraft 13 170 1% 23.8 52.8 36.7

Control First Stage AMS anthraquinone-2monosulphonic acid Alkali charge for kraft cooks '70 effective alkali Alkali sulphide at 25% sulphidity Alkali charge for soda cooks 7:; sodium hydroxide Heating time to maximum temperature 1 hour Second Stage NaOH added to pulp at 27% consistency Oxygen treatment: pulp contained 0.2% magnesium ion. Oxygen pressure psi at C for 60 minutes.

A mixture of spruce and balsam fir wood chips was subjected to the following treatment sequence.

TABLE X Cooking c E I D E D Sample Liquor Permanchlorine chlorine Viscosity Brightness chlorine NaOH ganate dioxide NaOH dioxide Centipoise Elrepho on pulp on pulp Number on pulp on pulp on pulp 1 Kraft 3.0 1.45 1.6 0.6 19.8 87.0 2 Kraft 3.4 1.65 1.1 0.6 16.5 84.9 3 Kraft 3.4 1.65 1.0 0.6 20.0 85.1 4 Kraft 3.0 1.45 1.3 0.7 15.7 85.4 5 Soda 3.0 1.45 1.4 0.6 10.7 85.0 6 Soda 3.2 1.55 1.6 0.6 12.9 85.4 7 Soda 3.2 1.55 1.4 0.6 12.5 84.6 8 Soda 3.2 1.55 1.2 0.5 11.9 85.2 9 Kraft 4.76 2.35 3.4 1.2 0.5 0.3 26.5 88.0

Control C chlorination, pulp at 3% consistency at room temperature for 1 hour E caustic extraction, pulp at 10% consistency at 65C for 2 hours D chlorine dioxide treatment, pulp at 6% consistency at 70C for 3 hours TABLE X1 Cooking Tensile Burst Tear Viscosity Sample Liquor (Breaking Length) Factor Factor Centipoise KM 500 300 500 300 500 300 CSF CSF CSF CSF CSF CSF 1 Kraft 10.8 12.3 73 79 106 95 19.8 2 Kraft 10.6 11.9 66 82 91 81 16.5 3 Kraft 10.1 1 1.0 72 79 105 94 20.0 4 Kraft 11.0 11.6 70 81 89 81 15.7 5 Soda 9.9 11.0 60 73 98 93 10.7 6 Soda 9.7 11.5 60 75 121 91 12.9 7 Soda 9.9 10.8 65 77 105 93 12.5 8 Soda 10.2 1 1.0 65 72 99 90 1 1.9 9 Kraft 10.8 11.0 68 71 112 91 26.5

1 Control TABLE X11 Yield Comparison Between the Process of this Invention (Example 7, Samples 1, 2, 5 and 8) and a Conventional Kraft Process (Example 7 Sample 9) in Delignification of Deciduous Wood (Birch) This Invention Control Type of cook Soda Kraft Soda Kraft Kraft +AMS- +AMS Sample 5 1 8 2 9 Kappa Number 15 16 17 23.8 Yield on wood 51.4 57.6 55.4 61.6 52.8 Increase in yield l.4 4.8 2.6 8.8 compared to control on wood Increase in yield compared to control 2.4 8.6 5.9 l 1.7 adjusted to same Kappa Number on wood Adjustment of yield of the control to a yield corre- 1. The chips were cooked with soda liquor containing sponding to the kappa number of Samples 1, 2, 5 and percent by weight of sodium hydroxide based on 8 was carried out as in in Examples 1 to 4. The slope the weight of wood, the ratio of liquor to wood being of the plot of percent yield against kappa number was 4:1. The cook contained 0.1 percent by weight based 0.415 percent yield per kappa number. The adjusted on wood of anthraquinone-2-monosulphonic acid. yield values for the control (Sample 9) are as follows. The maximum temperature of the cook was 180C and was reached after 1 hour. The cook was main- TABLE XIII tained at 180C for 50 minutes. The kappa number of the product was 82.4.

pp Number Yield 2. The partially delignified wood was washed with fresh 15 490 water. {3 13;; 3. Without defiberization, the partially delignified wood was impregnated at room temperature with an a ueous soluti e nt 1 I Y wei ht of EXAMPLE 8 q on o a nlng 5 5 percent by g 7 sodium hydroxide and magnesium sulphate in an amount containing 0.2 percent magnesium ion based on the weight of partially delignified wood.

4. The alkaline wood was treated in a closed reactor in the presence of water at a consistency of 27 percent at 1 C for 50 minutes with oxygen under a partial pressure of 80 pounds per square inch. The deligni- 14 treated additionally with 0.1 percent by weight of -anthraquinone-2-monosulphonic acid (AMS). In all samples the liquor to wood ratio was 4:1. The maximum temperature of the cooks was in all cases 170C.

fled Product was obtained in a Yield of -3 PI 5 After digestion the partially delignified product was by weight based On he ma al from p With washed with water. The conditions of the cooks and the 2.0 percent screen rejects. The material had a ViSCOS- characteristics of the product pulp are shown in Table ity of 12 centipoise and a kappa number of 35.7. XIV,

TABLE XIV Sample Alkali Sulphidity Time to Retention Yield Screen Kappa Viscosity reach time at Rejects Number 170C 170C on wood cps Hours Hours on wood AMS 5 18 1 2 /2 55.7 0.8 241 26.7

5. The oxygen-treated product pulp of step 4 was sub- The products of Samples 1, 3 and 4 were treated, at jected to three bleaching steps: chlorination, caustic a consistency of 3 percent in water, with sodium hyextraction and chlorine dioxide treatment. droxide and magnesium sulphate in amount equal to Chlorination: Pulp at 3.0 percent consistency by 0.2% magnesium ion. The products were then pressed weight treated with 7.14 percent by weight chlorine to a consistency of 27 percent and treated in an oxygen for 1 hour at 25C. reactor with oxygen under a partial pressure of 80 psi Caustic Extraction: Pulp at 12 percent consistency for 50 minutes at 115C. The oxygen-treated material by weight treated with 3.57% sodium hydroxide for 30 was then treated for 2 minutes in a Cowles Dissolver 2 hours at 65C. with additional water. The product was then washed Chlorine dioxide treatment: Pulp at 6 percent consiswith water. The results are shown in Table XV which tency by weight treated with 1.0 percent chlorine diincludes data on Samples 2 and 5 for purposes of comoxide by weight for 3 hours at 70C. The bleached parison. Sample 2 is a conventional kraft cook; Sample product had a brightness of 85 (Elrepho) and a vis- 5 a conventional soda cook.

TABLE xv' NAOI-l Yield Yield Screen Viscosity Yield of Sample 2 Sample Rejects Kappa adjusted for Kappa Difference on pulp on wood cps Ngtm- Number of sample in yield 81 on wood on wood on wood cosity of 10.6 centipoise. The yield was 92.1% based The yield 9 Sample 2 (coflventioflal Kraft) was on the weight of the oxygen-treated pulp i.e. the re- Justed to a yleld corresponding to the kappa numbers duction in yield during bleaching was 7.9 percent. of Samples 3 4 and 5 as described for p g 1 am les. EXAMPLE 9 p Five portions of eastern cottonwood chips were subjected to differing delignification treatments. Eastern All 5 samples were next subjected to bleaching secottonwood is a low density deciduous wood, in distincquences. All samples were subjected to the sequence; tion to birch, a high density deciduous wood. In the first chlorination, caustic extraction with sodium hydroxide, step all portions were treated in a 3 liter digester with and treatment with chlorine dioxide. Samples 2 and 5 cooking liquor at a liquor to wood ratio of 4:1. The were subjected to the additional sequence; caustic exmaximum temperature of the cooks was 170C. Blow- 6O traction with sodium hydroxide, and treatment with down was simulated by a 2 minute residence time of the v chlorine dioxide. The material was washed with water product with added water in a Cowles Dissolver. after each bleaching step. The results are shown in Samples 1 and 2 were treated with kraft cooking liquor: Table XVI. Sample 3 to 5 with soda cooking liquor. The percentage of the sodium hydroxide alkali reagent is expressed in Samples 1 and 2 aseffective alkali:.in Samples 3 to 5 as weight percent sodium hydroxide. Sample 3 was The physical properties of the bleached products were measured. These are shown in Table XVII.

TABLE XVI 8' SAMPLE l 2 3 4 5 CI: 2.8 4.06 3.28 3.86 4.82 c Temp. C 25 25 25 25 hr Time 1 1 1 l l NaOH 1.4 2 1.6 1.9 2.81 C Temp. E 65 65 65 65 65 hr Time 2 2 2 2 2 C102 0.5 l 0.5 0.5 1 C Temp. D 70 70 70 70 70 hr Time 3 3 3 3 3 NaOH 0.6 0.5 "C Temp. E 65 65 hr Time 2 2 C102 0.5 0.5 C Temp. D 70 70 hr Time 3 2 Brightness 89.5 89.9 87.4 88.5 87.4 Reversion 5.0 2.6 4.1 4.0 3.1 cps Viscosity 24.3 40.9 17.0 21.3 16.5 Yield on pulp 93.8 94.7 95.2 95.6 95.0 Yield on wood 53.3 51.3 53.0 54.8 52.9 Yield less ield of 2.0 1.7 3.5 1.6

Sam 1e 2 Yield iess yield of Sample 5 0.4 1.6 0.1 1.9

TABLE XVII Tensile Burst Tear Bulk Sample Breaking Length Factor Factor cc/gm CSF CSF CSF CSF CSF CSF CSF CSF What we claim is: 35.0 percent by weight with oxygen or an oxygen- 1. A process for the delignification of lignocellulosic containing gas for 10 to minutes at a temperamateri l hi h mprises th st s of ture of 80C to C and a partial pressure of oxyl. treating lignocellulosic material in a closed reac- 4O gen 0f 0 0 00 pounds per Square inch, and

tion vessel with pulping liquor containing a reagent 5. washing the oxygen treated lignocellulosic mateselected from the group consisting of an alkali rial with water. metal hydroxide and a mixture of an alkali metal 2. A process as claimed in claim 1 wherein the lignohydroxide and an alkali metal sulphide, wherein cellulosic material is a coniferous species of wood. there is added to said pulping liquor 0.02 to 2.0 45 3. A process as claimed in claim 1 wherein the lignopercent, preferably 0.05% to 1.0% by weight, cellulosic material is a deciduous species of wood. based on the weight of the lignocellulosic material 4. A process as claimed in claim 1 wherein the pulpof a material selected from the group consisting of ing liquor employed in the first step contains 14.0 to anthraquinone mono sulphonic acid, anthraqui- 24.0 percent, preferably 18.0 to 20.0 percent by none disulphonic acid, alkali metal salts of said 50 weight, based upon the weight of the lignocellulosic acids and admixtures of aforesaid acids and salts, material, of alkali metal hydroxide. at a temperature in the range C to C for 5. A process as claimed in claim 1 wherein the pulpa period of not greater than 120 minutes and prefing liquor employed in the first step contains 8.0 to erably not greater than 90 minutes, the tempera- 14.0 percent, preferably 10.0 to 12.0 percent, by ture and period of treatment being adapted to pro- 55 weight of alkali metal hydroxide expressed as effective vide a pulp yield of 55 to 65 percent by weight, alkali, and 5.0 to 40.0 percent, preferably 20.0 to 30.0

2. displacing the pulping liquor from the lignocellupercent, by weight of alkali metal sulphide expressed as losic material with water, or an aqueous solution of percent sulphidity, the percentages based upon the alkali metal hydroxide, weight of lignocellulosic material.

3. treating the lignocellulosic material without prior 60 6. A process as claimed in claim 1 wherein during the defiberization at a consistency of 2.0 to 30.0 persecond step the pulping liquor is displaced from the ligcent by weight in aqueous suspension for 0.5 to 30 nocellulosic material by spent liquor from the oxygen minutes at 20C to 90C with 2.0 to 20.0 percent treatment of the fourth step of the process. by weight of alkali metal hydroxide. 7 A process as claimed in claim 1 wherein during the 4. treating the alkaline lignocellulosic material in 65 second step the pulping liquor is displaced from the ligaqueous medium at a consistency of from 3.0 to

nocellulosic material by white water.

8. A process as claimed in claim 1 wherein during the third step, 0.1 to 1.0 percent by weight of a magnesium salt is added to the lignocellulosic material, the percentage being based upon the weight of the lignocellulosic material. h

9. A process as claimed in claim 8 wherein the magnesium salt is magnesium chloride or magnesium sulphate.

10. A process as claimed in claim 1 wherein the alkali metal hydroxide is sodium hydroxide or potassium hydroxide.

11. A process as claimed in claim 1 wherein during the third step the alkali metal hydroxide is provided in 13. A process as claimed in claim 1 wherein the oxygen-treated lignocellulosic material produced thereby is subjected to a bleaching sequence.

14. A process as claimed in claim 13 wherein the bleaching sequencecomprises the successive steps of chlorination, caustic extraction and treatment with chlorine dioxide. 

1. A PROCESS FOR THE DELIGNIFICATION OF LIGNOCELLULOSIC MATERIAL WHICH COMPRISES THE STEPS OF
 1. TREATING LIGNOCELLULOSIC MATERIAL IN A CLOSED REACTION VESSEL WITH PULPING LIQUOR CONTAINING A REAGENT SELECTED FROM THE GROUP CONSISTING OF AN ALKALI METAL HYDROXIDE AND A MIXTURE OF AN ALKALI METAL HYDROXIDE AND AN ALKALI METAL SULPHIDE, WHEREIN THERE IS ADDED TO SAID PULPING LIQUOR 0.02 TO 2.0 PERCENT, PREFERABLY 0.05% TO 1.0% BY WEIGHT, BASED ON THE WEIGHT OF THE LIGNOCELLULOSIC MATERIAL OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF ANTHRAQUINONE MONO SULPHONIC ACID, ANTHRAQUINONE DISULPHONIC ACID, ALKALI METAL SALTS OF SAID ACIDS AND ADMIXTURES OF AFORESAID ACIDS AND SALTS, AT A TEMPERATURE IN THE RANGE 160*C TO 195*C FOR A PERIOD OF NOT GREATER THAN 120 MINUTES AND PREFERABLY NOT GREATER THAN 90 MINUTES, THE TEMPERATURE AND PERIOD OF TREATMENT BEING ADAPTED TO PROVIDE A PULP YIELD OF 55 TO 65 PERCENT BY WEIGHT,
 2. DISPLACING THE PULPING LIQUOR FROM THE LIGNOCELLULOSIC MATERIAL WITH WATER, OR AN AQUEOUS SOLUTION OF ALKALI METAL HYDROXIDE,
 2. displacing the pulping liquor from the lignocellulosic material with water, or an aqueous solution of alkali metal hydroxide,
 2. A process as claimed in claim 1 wherein the lignocellulosic material is a coniferous species of wood.
 3. A process as claimed in claim 1 wherein the lignocellulosic material is a deciduous species of wood.
 3. treating the lignocellulosic material without prior defiberization at a consistency of 2.0 to 30.0 percent by weight in aqueous suspension for 0.5 to 30 minutes at 20*C to 90*C with 2.0 to 20.0 percent by weight of alkali metal hydroxide.
 3. TREATING THE LIGNOCELLULOSIC MATERIAL WITHOUT PRIOR DEFIBERIZATION AT A CONSISTENCY OF 2.0 TO 30.0 PERCENT BY WEIGHT IN AQUEOUS SUSPENSION FOR 0.5 TO 30 MINUTES AT 20*C TO 90*C WITH 2.0 TO 20.0 PERCENT BY WEIGHT OF ALKALI METAL HYDROXIDE.
 4. TREATING THE ALKALINE LIGNOCELLULOSIC MATERIAL IN AQUEOUS MEDIUM AT A CONSISTENCY OF FROM 3.0 TO 35.0 PERCENT BY WEIGHT WITH OXYGEN OR AN OXYGEN-CONTAINING GAS FOR 10 TO 120 MINUTES AT A TEMPERATURE OF 80*C TO 140*C AND A PARTIAL PRESSURE OF OXYGEN OF 30 TO 200 POUNDS PER SQUARE INCH, AND
 4. treating the alkaline lignocellulosic material in aqueous medium at a consistency of from 3.0 to 35.0 percent by weight with oxygen or an oxygen-containing gas for 10 to 120 minutes at a temperature of 80*C to 140*C and a partial pressure of oxygen of 30 to 200 pounds per square inch, and
 4. A process as claimed in claim 1 wherein the pulping liquor employed in the first step contains 14.0 to 24.0 percent, preferably 18.0 to 20.0 percent by weight, based upon the weight of the lignocellulosic material, of alkali metal hydroxide.
 5. A process as claimed in claim 1 wherein the pulping liquor employed in the first step contains 8.0 to 14.0 percent, preferably 10.0 to 12.0 percent, by weight of alkali metal hydroxide expressed as effective alkali, and 5.0 to 40.0 percent, preferably 20.0 to 30.0 percent, by weight of alkali metal sulphide expressed as percent sulphidity, the percentages based upon the weight of lignocellulosic material.
 5. washing the oxygen treated lignocellulosic material with water.
 5. WASHING THE OXYGEN TREATED LIGNOCELLULOSIC MATERIAL WITH WATER.
 6. A process as claimed in claim 1 wherein during the second step the pulping liquor is displaced from the lignocellulosic material by spent liquor from the oxygen treatment of the fourth step of the process.
 7. A process as claimed in claim 1 wherein during the second step the pulping liquor is displaced from the lignocellulosic material by white water.
 8. A process as claimed in claim 1 wherein during the third step, 0.1 to 1.0 percent by weight of a magnesium salt is added to the lignocellulosic material, the percentage being based upon the weight of the lignocellulosic material.
 9. A process as claimed in claim 8 wherein the magnesium salt is magnesium chloride or magnesium sulphate.
 10. A process as claimed in claim 1 wherein the alkali metal hydroxide is sodium hydroxide or potassium hydroxide.
 11. A process as claimed in claim 1 wherein during the third step the alkali metal hydroxide is provided in the form of white liquor or oxidized white liquor.
 12. A process as claimed in claim 1 wherein during the third step the lignocellulosic material is at a consistency of 2 to 6 percent by weight.
 13. A process as claimed in claim 1 wherein the oxygen-treated lignocellulosic material produced thereby is subjected to a bleaching sequence.
 14. A process as claimed in claim 13 wherein the bleaching sequence comprises the successive steps of chlorination, caustic extraction and treatment with chlorine dioxide. 